Electrical control circuit



June 8, 1948. P. c. SMITH ELECTRICAL CONTROL CIRCUIT Filed May 26, 1944 PHIL/P5 4 0 125 INVEIYTOR. 1 & Jmdh ,97T0MY Par BY Patented June 8, 1948 Perry 0. Smith, Moorestown, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application May as, 1944, Serial No. 537,501

Claims.

1 This invention relates generally to electrical power control apparatus and more particularly to an improved marginal relay circuit for controlling the energization of a load device.

The invention will be explained hereinafter, by way 0! example, as an improvement upon the system disclosed and claimed in the copending U. 8. application of Igor E. Grosdoil', Serial No. 448,254, filed June 24, 1942, now United States Patent No. 2,383,600, issued August 28, 1945, entitled Vacuum gauge electric power supply interlock," and assigned to the same assignee as the instant application.

Heretoiore, various types of pressure gauges have been utilized for indicating gas pressure or vacuum conditions within a sealed chamber. Among the most satisfactory devices for measuring the pressure at comparatively high vacuums is the well known ionization type gauge of which an extremely practical modification is known as the Phillips gauge. These devices and their applications are described in considerable detail in an article entitled High-vacuum gauges by F. M. Penning in PhilipNTechnical Review, vol. II, No. 7 for July l937, on pages 201 to 208, inelusive.

The device disclosed in the copending application, identified heretofore,'contemplates the use oi a plurality of diiierent types of vacuum gauges for indicating the gas pressure within a sealed chamber over the eflective ranges of the various gauges, including an electrical circuit associated with the Philips gauge for controlling the energization of a power circuit. Such a vacuum gauge-power interlock has great utility in the operation of an electron microscope, or similar device, in which an incandescent filament is en closed within an evacuated container, the vacuum of which at times must be reduced to atmospheric pressure during the operation of the device. In applications oi this type, serious damage to the incandescent filament may result unless some automatic means is provided for deenergizing the filament when air is introduced into the container. The circuit described may be energized, either partially or completely, from a source 0! alternating potential, thereby providing a simple and convenient system for accomplishing the control described heretofore.

The instant invention contemplates the use of an improved relay circuit responsive to a Philips gauge or other control circuit, wherein the sensitlvlty of the relay to slight variations in energizing currents therefor is substantially increased. It is well known that conventional electromagnetic relay devices which require a predetermined energizing current for actuating the armature thereof will retain said armature in the pull-down position until the energizing current is reduced substantially below the value necessary for initial attraction of the armature. Therefore, apparatus of the type described in said copending application will provide actuation oi. the relay armature at one predetermined vacuum condition, while the armature will not be released until the vacuum has changed to a substantially diiierent value than that required for its initial actuation. This condition is due to residual magnetism inherent in conventional relay magnetic structures.

The purpose of the instant invention is to provide a compensating circuit, actuated by movement of the relay armature, whereby the sensitivity of the relay remains substantially constant regardless of its operating condition. Briefly, the invention comprises a novel combination 0! resistors and auxiliary relay contacts whereby initial attraction of the relay amiature by the relay solenoid actuates a single-pole double-throw contact switch arrangement to reduce the current flow through the relay winding and in addition to compensate for the resultant diiference in voltage drop across the relay winding thereby to provide substantially constant voltage across the relay actuating power circuit.

Among the objects of the invention are to provide an improved method of and means for controlling the operation of a power control relay. Another object of the invention is to provide an improved means forcontrolling a power circuit in response to a thermionic tube control circuit. A further object of the invention is to provide an improved vacuum gauge-thermionic tube power interlock network wherein an ionization type gauge responsive to gas pressure controls a thermionic tube having a power control relay in its output circuit and wherein the marginal operational limits otthe relay are controlled by a novel compensating network. An additional object 0! the invention is to provide improved means for controlling the marginal operational limits of an electromagnetic relay device.

The invention will be described by reference to the accompanying drawing of which the single figure is a schematic circuit diagram of a preferred embodiment thereof.

Referring to the drawing, one terminal of a Philips vacuum gauge! is connected, through a high resistance 2, to one terminal of a high voltage secondary winding 3 of a conventional discharge tube 6, which may be of the well known neon type having a pair of electrodes. The remaining terminal of the gas discharge tube 6 is connected to one terminal of a bypass condenser 1, and to one terminal of a second resistor 8. The

. remaining terminal of the second resistor 8 is connected, through a sensitive D.-C. meter 9, to "-the remaining terminal of the capacitor 1, and

to the remaining terminal of the high voltage secondary winding 3. A third resistor it] may be connected across the extremely sensitive meter 9, if desired.

The terminals of the second transformer secondary winding H are connected, respectively, to the two anodes of a double-diode rectifier tube l2. The two cathodes of the diode rectifier tube i2 are connected, through a second capacitor I3, to the electrical center tap of the second transformer secondary winding H, and to the control electrode of a'thermionic amplifier tube I4. A third resistor I is connected in parallel with the second capacitor 13, and is also connected to the common terminal of the meter 9 and the high voltage secondary winding 3. The heater elements of the double-diode tube i2 and the amplifier tube H are supplied with alternating current from a low voltage secondary winding it, provided therefor on the first transformer. If desired, connections may be provided from the low voltage secondary winding It to energize a power indicator such as a lamp l1.

The cathode of the amplifier tube I4 is connected through a fourth resistor l8 to the common terminal A of the meter 9 and the high voltage transformer secondary winding 3. This common terminal A is connected through a first switch l9 and a fifth resistor 23 to ground. One terminal of a voltage regulator tube 2| is connected through a second switch 22 to the cathode and the remaining terminal thereof is connected to ground. The positive terminal of a. source of anode potential B is connected through a third switch 23 to one terminal C of a sixth resistor 24, the remaining terminal of which is connected to the cathode electrode of the amplifier tube i4. The negative terminal of the anode voltage supply B is grounded.

The terminal C of the sixth resistor 24 is connected, through a variable high resistor 25 and a serially-connected adjustably-tapped resistor 26, to the screen electrode of the amplifier tube l4. The winding 21 of an electromagnetic relay 28 is connectedbetween the screen and anode electrodes of the amplifier tube. A second adjustably-tapped resistor 23 is connected across the relay winding 21.

The relay 28 includes two sets of movable contacts 30, 3| which are insulated from each other but simultaneously actuated by energization of the relay winding 21.

One terminal of the microscope electron gun or any other auxiliary load circuit 32 is con-,

nected to ground. The remaining terminal of the gun is connected, through a pressure responsive switch 33, located in the enclosedchamber 34, and through the relay contacts 30, 35, to the positive terminal of the anode potential source. It should be understood, of course, that any other type of load circuit including a separate power source could be controlled in the same manner.

In operation, when the pressure chamber 34 is evacuated to a predetermined degree, the contacts of the pressure responsive switch .33 are closed. As the vacuum increases, the Philips gauge I passes an A.-C. potential or current which decreases in proportion to the decrease in gas pressure. This alternating current flows through the gas tube 6 and thereby provides illumination at both terminals of the gas discharge tube. The alternating current is bypassed by the condenser 1 around the meter 9 so that no indication is provided thereby.

As the gas pressure is reduced to the order of 10 microns, the Philips gauge becomes a rectifier, and transmits thereafter only pulsating D.-,C. current. The polarity of the Philips gauge merely determines the polarity of the meter 3. This pulsating D.-C. current provides illumination of only one terminal of the gas discharge tube 6, which illumination gradually. decreases as the gas pressure in the chamber is progressively reduced.

The voltages induced in the secondary winding ll of the second transformer by the alternatin or pulsating currents in its primary winding are rectified by the double-diode tube I2 to provide a positive bias on the control electrode of the amplifier tube 14, thereby energizing the relay winding 21 and opening the load circuit contacts 33, 35. I

When the gas pressure in the container drops below a predetermined value, for example 5 microns, the positive potential on the control electrode of the amplifier tube i4 decreases beyond a critical value so that the normally negative grid bias potential thereon, blocks the tube and de-energizes the relay 28, closing the load circuit contacts 30 and 35. It should be understood that the polarity of the diode [2 may be reversed, and reversed relay action utilized to control the load circuit energization. The re-' sistor network comprising the resistors I9, 20 and 24 and the voltage regulator tube 2| provide, in a well known manner, a substantially constant negative control electrode bias potential for the amplifier tube l4. v

If it is desired to operate the circuit entirely from alternating potentials, the power source B, the resistor 20 and the voltage regulator 2| may be disconnected, and a source of alternating potential may be connected between the terminals A and C, by means of the switches I9, 22 and 23, which may be ganged to operate simultaneously, as indicated by the dash line 36.

The second movable contact 3| of the relay 28 normally contacts a first fixed relay contact 31 which is connected to the adjustable contact 38 on the first adjustable resistor 23, thereby shortcircuiting a portion of the resistor when the relay is de-energized. When the relay armature is By adjustment of the taps l and "on the adjustable tapped resistors 29, 26, respectively, the relay may be caused to open and close the load contacts 30, 35 in response to very slight variations in the voltage derived from the Philips gauge I and applied to the amplifier tube l4.

age drop across by operation of Also, although thevoltthe relay winding 21 is varied the relay contacts ll, 39, the efi'ective' voltage appl ed to the amplifier tube anode may be maintained substantially constant due to the compensating action of the relay contacts ll, 31 connectedacross the portion of the series resistor 26. This latter feature is particularly desirable when pentode or constant current type tubes are not employed for the relay actuating amplifier. 1

The variable high resistor 25 may be adjusted to provide coarse control of the relay operating range prior to the fine adjustment thereof by means of the adjustable contacts and the adjustable resistors 26 and 29.

Thus the invention disclosed comprises an improved method of and means for controlling the sensitivity of an electromagnetic power control relay, wherein compensating resistors, controlled by contacts on said relay, permit the marginal limits of the relay actuating currents to be adjusted over a. predetermined wide or, narrow range, and wherein said compensating elements may be adjusted to provide substantially constant load upon the relay energizing source. It should be understood that any known type of relay control and energizing system may be employed, and that the invention is not necessarily limited to vaeuumtube relays oi the general type described heretofore.

I claim as my invention:

1. An electrical marginal control circuit including an electromagnetic relay device having a solenoid winding and means for controlling a load device, connecting means for a source of current for selectively energizing said winding to actuate said load controlling means, a first resistor connected to said winding, a second resistor connected to said winding, single pole-double throw contact means on said device operable in response to said selective energization of said winding and connected to said resistors for selectively adjusting the eflective resistance of said first resistor upon energization of said winding for adjusting said energizing current to control the marginal operation oi. said relay device and for adjusting the eilective resistance of said second resistor upon deenergization of said winding for simultaneously maintaining substantially constant the loading of said current source.

2. An electrical marginal control circuit including an electromagnetic relay device having a solenoid winding and means for controlling a load device, connecting means for a source of current for selectively energizing said winding to actuate said load controlling means, a first resistor shunting said winding and having an intermediate connection thereon, a second resistor having an intermediate tap and serially connected with said winding, single pole-double throw contact means on said device operable in response to said selective energization of said winding and connected to said intermediate taps on said resistors for selectively short-circuiting a portion of said first resistor upon energization of said winding for adjusting said energizing current to control the marginal operation of said relay device and for short-circuiting a porthe control electrode of tion of said second resistor upon deenergization or said winding for simultaneously maintaining substantially constant the loading of said current source.

3. An electrical marginal control circuit including an electromagnetic relay device having a solenoid winding and means for controlling a load device, connecting means for a source or current for selectively energizing said winding to actuate said load controlling means, a first impedance device connected to said winding and having an intermediate connection thereon, first contact means on said device operable in response to said selective energization of said winding and connected to said intermediate tap on said impedance device for selectively adjusting the portion of said impedance device connected to said winding upon energization of said winding for adjusting said energizing current to control the marginal operation of said relay device, a second impedance device connected with said winding and having an intermediate connection thereon, and second contact means on said device operable in response to said winding energizing current and connected to said intermediate tap on said second impedance device for adjusting the impedance of said second impedance device upon deenergization of said winding for simultaneously maintaining substantially constant the loading of said current source.

4. An electrical marginal control circuit including an electromagnetic relay device having a solenoid winding and means for controlling a load device, connecting means for a source of current for selectively energizing said winding to actuate said load controlling means, a resistor shunting said winding and having an intermediate connection thereon, first contact means on said device operable in response to said selective energization of said winding and connected to said intermediate tap on said resistor for selectiveiy short-circuiting a portion of said resistor upon energization of said winding for adjusting said energizing current to control the marginal operation of said relay device, a second resistor serially connected with said winding and having an intermediate connection thereon, and second contact means on said device operable in responseto said winding energizing current and connected to said intermediate tap on said second resistor for short-cireuiting a portion of said second resistorupon deenergization of said winding for simultaneously maintaining substantially constant the loading of said current source.

5. An electrical marginal control circuit including an electromagnetic relay device having a solenoid winding and means for controlling a load device, connecting means for a source of current for selectively energizing said winding to actuate said load controlling means, a resistor shunting said winding and having an intermediate connection thereon, a movable contact means on said device operable in response to said selective energization of said winding, a first fixed contact operatively disposed adjacent said movable contact and connected to said intermediate tap on said resistor for selectively short-circuiting a portion 01' said resistor upon energization of said winding for adjusting said energizing current to control the marginal operating current limits or said end resistor serially connected with said winding and having an intermediate connection thereon, and second fixed contact means on said device operatively disposed adjacent said movable relay device, a seccontact and connected to said intermediate tap on said second resistor for short-circuiting a portion or said second resistor upon deenergiza- Numb r tion 01' said winding for simultaneously main- 1,105,187 taining substantially constant the loading of said 5 1. .8 2 current source. 2.086.060 2,087,783 PERRY c. SMITH. 4 2,278,697 REFERENCES CITED 19 2,285,152 2,350,938 The following references are of record in the 2,383,600

file of this patent:

UNITED STATES PATENTS Name Date Bosau Aug. 4, 1914 Simon June 15, 1915 Appleyard et a1 July 6, 1937 Savage July 20, 1937 Buch et al Nov. 5,1940 Gould Apr. '1, 1942 Firestone June 2, 1942 Sparrow June 6, 1944 Grosdofl Aug. 28, 1945 

